Process for treatment of oil-wax mixtures



June 15, 19377. J. A. ALEXANDER PROCESS FOR TREATMENT OF OIL WAX MIXTURES 7 Solve/2532 'Dzlr Tani an Z LEE frzven for Joseph Au4lexander lzz's Aiiorney Patented June '15, 1937 UNITED STATES PATENT OFFICE PROCESS FOR TREATMENT OF OIL-WAX MIXTURES Joseph A. Alexander, Philadelphia, Pa., assignor to The Atlantic Refining Company, Philadelphia, Pa, a oorporationof Pennsylvania Application January 30, 1935, Serial No. 4,159

11 Claims.

in the co-pending application of S; W. Ferris,

Serial No. 4,157, filed January 30, 1935.

Briefly, the process disclosed in the co-pending application of Ferris consists in preparing an oilwax mixture, as for example, by distillation,

which upon'cooling to the desired separating temperature, will crystallize wax to the extent of substantially 10% or less of the total volume of the mixture; or the dilution of a Wax-bearing stock with a suitable solvent, so that upon cool- 15 ing to the desired separating temperature, wax

will crystallize to the extent of 10% or less of the total volume of the mixture. The oil-wax mixture so prepared is then cooled to the desired temperature, with or without agitation, in such a manner as to effect dispersion of the wax crystals throughout the mother liquor withreasonable uniformity. If agitation is resorted to, thereafter the cooled mother liquor containing the wax crystals is permitted to stand unagitated for sufficient time to effect the formation of a porous wax mass containing less than substantially 10% of solid wax per unit volume-of the mass, the structure of which has appreciable mechanical strength. Displacement of the mother liquor from the cooled wax mass is then accomplished by passing a displacing liquid, preferably an oil solvent, through the mass in such a manner that a substantially horizontal interface is maintained between the mother liquor in the mass and the displacing liquid, the displacement pressure (differential pressure or pressure dropthrough the wax mass) being of the order of 5 lbs;/sq. in., or less per foot depth of wax 7 mass, and the concentration of crystalline wax 40 being less than substantially 20% by volume of the mass in which mother liquor is still present. The displacement step is usually accompanied by the settling or compacting of the wax mass from which the mother liquor is being removed,

but such compacting is controlled to prevent the concentration of crystalline Wax in the mass from exceeding substantially 20% by volume of the mass. This control is obtained by the proper adjustment of the quantity of wax crystallized from the mother liquor to form the initial wax mass, the rate and degree of cooling, the differential pressure, required for displacement and the gravity differentials between wax, mother liquor and displacing liquid. Upon completion of the displacement operation, the'solvents employed may be separated respectively from the oil and wax fractions by distillation.

In carrying out the process, it is necessary to control the quantity of wax in the mother liquor so that the crystalline wax which forms the porous wax mass resulting from the chilling of the,

mother liquor will not constitute substantially more than 10% of any unit volume of the mass at the beginning of the displacement operation. In most instances, it has been found that the crystalline wax constituting the wax mass at the beginning of the displacement step should be of the order of from 1% to 6% of the mass by volume, and preferably of the order of from 2.5% to 4.5% by volume; it may, however, be as high as 10% by volume depending upon the character of the wax crystals. Furthermore, in general, the differential pressure required in effecting displacement does not exceed substantially 5 lbs/sq. in. per unit (1 foot) depth of the wax mass, and usually at the outset does not exceed 2 lbs/sq. in. It is to be understood, however, that at some stage of the operation, and

particularly during the latter part thereof, the

pressure may be somewhat in excess of 5 lbs/sq. in. per 1 foot depth of the mass.

I have found that satisfactory displacement of mother liquor from the wax'mass may be effected by employing a volume of displacing or washing liquid substantially less than that of the wax mass from which the mother liquor is to be removed. In other words, I have found it unnecessary to employ a volume of displacing liquid equal to or in excess of the volume of the wax mass, and that in utilizing a smaller volume of displacing liquid, I effect displacement in such a manner that the entire volume of liquid em ployed will have penetrated into the wax mass and will have left the surface thereof relatively free of liquid, before the displacement of the mother liquor has been completed. The volume of displacing or washing liquid employed is of the order of about 15% to about and preferably of the order of about 30% to about 40%, of the volume of the wax mass from which the mother liquor is to be displaced.

In accordance with my invention, a wax mass is formed in the mother liquor contained in a displacement vessel, under such conditions that the wax crystals occupy a relatively small proportion volume of the mass, 1. e., less than 10% by volume, and are distributed substantially uniformly thruout the mass. A quantity of displacing liquid, preferably of the order of from 30% to 40% by volume of the wax mass containing the mother liquor, is placed upon the upper surface thereof, in toto or in increments, and the mother liquor is displaced from the mass. The displacement may be effected under the influence of the head of displacing liquid alone, or together with the application of slight pressure above the surface of the displacing liquid. As the displacing liquid penetrates into the wax mass and the upper surface of the liquid reaches the upper surface of the wax mass, such surface is exposed to the air or other gas contained in the displacing vessel. Inasmuch as the air above the wax mass does not enter the mass, the upper portion thereof is compressed to a certain extent, and thereafter acts as a fluid piston which forces the mother liquor from the remainder of the unwashed mass. The entire quantity of displacing liquid enters the wax mass, thus leaving no liquid head above the surface thereof, before displacing liquid appears as cffluent and the displacement is completed.

For example, if the displacement vessel contains a wax mass consisting of parts by volume of mother liquor and 5 parts by volume of solid wax, and it is desired to remove the mother liquor therefrom with 35 parts by volume of displacing liquid, the displacement will preferably be carried on until the displacing liquid begins to appear at the eiilux outlet of the vessel. The wax mass, at the completion of the displacement will consist of approximately 35 parts by volume of displacing liquid and 5 parts by volume of solid wax. Thus, the wax mass will have been compacted to about 40% of its initial volume, during the displacement of substantially all of the mother liquor which was contained in the initial wax mass.

In addition to the savings involved in employing a small volume of displacing liquid, 2. further advantage resides in my invention in that the formation and/0r growth of cracks or channels in the wax mass during displacement is substantially reduced. By maintaining a relatively small head of displacing liquid above the surface of the wax mass during the initial steps of the displacement, cracks or channels which may develop during the displacing operation will not be aggravated or extended to a degree as great as that when a large head of liquid is employed. Furthermore, when the upper surface of the displacing liquid has reached or penetrated beneath the upper surface of the wax mass, there will be little or no tendency for vertical cracks or channels to be extended or enlarged, since there is no head of liquid to feed such cracks or channels.

For a clearer understanding of my invention, reference is made to the accompanying drawing which shows an apparatus suitable for carrying on my process.

From a steam jacketed stock tank l, 40 parts, for example, of a wax bearing distillate from East Texas crude oil having a pour test of 125 F., and a Saybolt universal viscosity of 60 seconds at 210 F., is withdrawn through valve-controlled pipe 2 and pumped by pump 3 through valve-controlled pipe t into mixing tank 5 provided with heating coil 6 and stirrer l. Simultaneously or subsequently, 60 parts, for example, of ethylene dichloride is withdrawn from solvent tank 8 by means of valve-controlled pipe 9 and pumped by pump It through valve-controlled pipe 4 into mixing tank 5. Herein the solvent and distillate containing wax is agitated at a temperature of,

for example, F., until a homogeneous solution is obtained. The resulting solution is passed from the mixing tank 5 by means of valve-controlled pipe I l and is pumped by pump I2 thru valve-controlled pipe I3 to chilling device l4, wherein the solution is cooled until the temperature is of the order of, for example, 85 F., and a portion of the wax has crystallized. This oilwax-solvent mixture is passed from the chiller I 4 by means of valve-controlled pipe l5 into the brine-jacketed displacement tower l6 above the screen l'l. Prior to the introduction of the chilled mixture into the tower l6, air pressure is applied to brine tank 5 B through valve-controlled pipe l9 provided with valved vent HM and brine is forced through valve-controlled pipe 20 and pipe 24 into the conical lower section of tower I6 until it barely covers the screen IT. The brine and screen I? thus support the chilled oil-waxsolvent mixture in the tower it. The mixture contained in the displacement tower I6 is then cooled at the rate of, for example, 1 F. to 4 F. per hour until the temperature of the mixture is of the order of, for example, 65 F., and the desired final quantity of wax has crystallized out. The cooling in the tower l6 may be effected by circulation of cold brine in the tower jacket and/ or by the employment of brine coils or pipes (not shown) installed within the tower.

The mixture is preferably allowed to remain in a quiescent state within the tower 16 during the final cooiing period, in which time the wax crystals form an agglomerate mass of appreciable strength while still retaining a high degree of free space or porosity thruout which the mother liquor is distributed. At the completion of the cooling period, 40 parts of a displacing liquid, for example, naphtha of 50 A. P. I. gravity, is passed from the displacement liquid tank 22 through valve-controlled pipe 23, cooled to about 65 F. in cooling coil 2 1, and introduced into the displacement tower is by means of valve-controlled pipe 25, above the surface of the chilled oil-wax-solvent mixture contained therein. The displacing liquid is introduced in such a manner as to prevent substantial disturbance of the wax mass from which the oil and solvent are to be displaced. Preferably simultaneously with the introduction of the displacing liquid at the top of tower l6, brine is withdrawn from the bottom of said tower and returned to the brine tank M by means of valve-controlled pipe 20; Oil and solvent from the wax mass, displaced downwardly by the incoming displacing liquid, is withdrawn from the bottom of tower is and passed through valve-controlled pipes 26 and 27 into receiving or heavy efllux tank 28. Before the displacement is completed, substantially all of the displacing liquid, i. e., the 40 parts of 50 naphtha, has penetrated into the wax mass, leaving the upper surface thereof substantially free of liquid. If necessary, slight pressure may be applied to the tower l6, above the level of its contents, by means of valve-controlled air line 29 provided with valved vent The differential or displacement pressure should preferably be maintained at less than 5 lbs/sq. in. per 1 foot depth of the wax mass, in order to prevent undue compacting of the wax crystals. When substantially all of the oil and solvent (heavy efflux) has been displaced from the wax mass into receiving tank 28., as evidenced by a marked change in gravity or other critical property of the liquid issuing from the tower IS, the liquid thereafter withdrawn from the tower is diverted into receiving or light efilux tank 3| by closing valve-contolled pipe 21 and opening valve-controlled pipe 32. This light efflux will consist primarily of displacing liquid containing residual oil and solvent which has been washed from the wax mass. The displacing or washing operation is preferably continued until the eflluent from' tower i6 is principally displacing liquid.

' At the completion of the displacing or washing operation, the wax mass containing residual displacing liquid is forced upwardly and out of tower I 6 through valve-controlled pipe 33 into wax receiving tank 34, by means of brine introduced into the bottom of the tower from brine tank l8. If necessary, the Wax mass contained in tower l6 may be rendered more fluid by the application of steam in the jacket surrounding said tower. The heavy efilux (oil and solvent) in tank 28, the light efilux (oil, solvent and displacing liquid) in tank 3|, and the wax con taining residual displacing liquid may be withdrawn from their respective receiving tanks by means of valve-controlled pipes 35, 36 and 31 and passed to distilling apparatus (not shown) wherein the solvent, 1. e., ethylene dichloride and the displacing liquid, i. e., naphtha, may be separated and recovered from the oil and wax.

While in the above instance, I have described the chilling of the solution of oil stock and solvent from the mixing tank as being effected partially within the chiller M and partially within the displacement tower I6, I may, if desired, pass the heated solution from the mixing tank 5 directly to the tower l6 by means of valve-controlled by-pass 38 and effect such chilling entirely within the tower IE, or I may chill the solution entirely in the chiller [4 prior to the introduction thereof into the displacement tower it, The latter method of operation may be carried out by pumping the heated solution directly from mixing vessel 5 through valve-controlled pipe l3, chiller l4 and valve-controlled pipe Iii into tower iii. In this instance, the chilled mixture is preferably allowed to remain in a quiescent state within tower I6 for a period of, for example, 4 hours, 1

during which time the crystals form an agglomerate mass having appreciable mechanical strength while still retaining a high degree of free space thruout which the mother liquor is distributed. Due to the gravity differential between the wax and the mother liquor a certain amount of upward settling of the former occurs, so that at the end of the quiescent period a lower layer of relatively wax-free oil solution is present which may be about 30% of the volume of the total charge. This layer is drawn off from the bottom, at the same time the wax mass settles until upon completion of the removal of the wax-free solution, the bottom of the wax mass rests upon the screen. The displacement step is then carried on as above described.

The process above described is given as exemplary of the separation of hydrocarbon oi1-wax mixtures by downward displacement. However, it is to be understood that the employment of small volumes of displacing liquid, i. e., 15% to 60% by volume of the wax-containing mixture charged to the displacement vessel, may be equally well applied to the separation of oil-wax mixtures by upward displacement. In the latter instance, the displacing liquid is preferably of greater specific gravity than the wax-containing mixture and is introduced at the bottom of the displacement vessel, beneath the mixture contained therein. The displacement may be effected by introducing brine beneath the layer of displacing liquid and forcing the latter upwardly into and thru the wax mass, the mother liquor from such mass being discharged from the top of the displacement vessel.

In the description of my process given hereinabove, I have shown that ethylene dichloride may be employed as the crystallizing solvent and naphtha as the displacing liquid. In addition thereto, I may also employ conventional dewaxing solvents, such as acetone, acetone-benzol, alcohols, esters, ethers, halogenated hydrocarbons and liquefied normally gaseous hydrocarbons.

For brevity, in the appended claims, the terms solvent liquid and displacing liquid are to be understood to comprehend those compounds in which oil is readily miscible and wax is relatively immiscible at the temperatures employed in the separation of the oil and wax. Also, the term wax mass as employed herein and in the appended claims comprehends a porous mass or body of wax crystals containing oil or oil and solvent distributed therethrough.

What I claim is:

1. The process of separating a hydrocarbon oilwax mixture into solid constituents and liquid constituents, which comprises producing a waxcontaining mixture, cooling said mixture to effect crystallization of wax to form a porous wax mass containing less than substantially 10% by volume of solid wax and displacing from said porous wax mass, without substantial compression of that portion of the wax mass from which displacement has not been effected, the liquid constituents of said mass with such quantity of displacing liquid that said liquid will completely enter the wax mass before displacement is completed.

2. The process of separating a hydrocarbon oilwax mixture into solid constituents and liquid constituents, which comprises producing a waxcontaining mixture, coolingsaid mixture to effect crystallization of wax to form a wax mass containing less than substantially 10% by volume of solid wax and displacing from said wax mass, without substantial agitation thereof, and under a low differential pressure, the liquid constituents of said mass with a quantity of displacing liquid equal to about to of the volume of said mass.

3. The process of separating a hydrocarbon oilwax mixture into solid constituents and liquid constituents, which comprises producing a waxco-ntaining mixture, cooling said mixture to crys-. tallize wax to form a wax mass containing about 1% to about 6% by volume of solid wax and displacing from said mass, without substantial agitation thereof and under a relatively low differential pressure, the liquid constituents of said mass with a quantity of displacing liquid equal to about 15% to 60% of the volume of said mass.

4. The process of separating a hydrocarbon oilwax mixture into solid constituents and liquid constituents, which comprises diluting said mixture with a solvent liquid, cooling the diluted mixture to effect crystallization of wax to form a porous wax mass containing less than substantially 10% by volume of solid wax and displacing from said porous wax mass, without substantial compression of that portion of the wax mass from which displacement has not been effected, the liquid constituents of said mass with such quantity of displacing liquid that said liquid will completely enter the wax mass before displacement is completed.

5. The process of separating a hydrocarbon oil-Wax mixture into solid constituents and liquid constituents, which comprises diluting said mixture with a solvent liquid, cooling the diluted mixture to effect crystallization of wax to form a wax mass containing less than substantially 10% by volume of solid wax and displacing from said wax mass, without substantial agitation thereof, and under a low differential pressure, the liquid constituents of said mass with a quantity of displacing liquid equal to about 15% to 60% of the volume of said mass.

6. The process of separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises adding to said mixture a solvent liquid, heating such admixture to a temperature suflicient to effect solution, cooling the solution to effect crystallization of wax to form a porous wax mass containingless than substantially 10% by volume of solid wax and displacing from said porous wax mass, without substantial compression of that portion of the wax mass from which displacement has not been effected, the liquid constituents of said mass with such quantity of displacing liquid that said liquid Will completely enter the wax mass before displacement is completed.

7. The process of separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises adding to said mixture a solvent liquid, heating such admixture to a temperature sufficient to effect solution, cooling the solution to efiect crystallization of wax to form a wax mass containing less than substantially 10% by volume of solid wax and displacing from said wax mass, without substantial agitation thereof, and under a low differential pressure, the liquid constituents of said mass with a quantity of displacing liquid equal to about 15% to 60% of the volume of said mass.

8. The process for separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises adding to the oil-wax mixture a solvent liquid, heating the admixture to a temperature sufiicient to effect solution, cooling the solution to crystallize therefrom less than substantially 10% by volume of solid wax, passing the solution containing the crystallized wax into a displacing zone to form a wax mass of substantial uniformity introducing a quantity of displacing liquid equal to about 15% to 60% of the volume of said mass into said zone while preventing substantial agitation of the wax mass and passing said displacing liquid through said wax mass, without substantial agitation thereof and under a low differential pressure to displace therefrom the liquid constituents contained therein.

9. The process for separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises adding to the oil-Wax mixture a solvent liquid, heating the admixture to a temperature sufficient to effect solution, partially cooling said solution to crystallize therefrom a portion of the wax, passing the solution containing the crystallized wax into a displacing zone, cooling said solution to effect a further crystallization of wax to form a wax mass of substantial uniformity containing less than substantially 10% by volume of solid wax, introducing a quantity of displacing liquid equal to about 15% to 60% of the volume of said mass into said zone While preventing substantial agitation of the wax mass and passing said displacing liquid through said wax mass, without substantial agitation thereof and under a low differential pressure, to displace therefrom the liquid constituents contained therein.

10. The process for separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises adding to the oil-wax mixture a solvent liquid, heating the admixture to a temperature sufficient to effect solution, passing the solution so formed into a displacing zone, cooling the solution, without substantial agitation, to efiect crystallization of a wax mass containing less than substantially 10% by volume of solid wax, introducing a quantity of displacing liquid equal to about 15% to 60% of the volume of said mass into said zone while preventing substantial agitation of the wax mass and passing said displacing liquid through said wax mass, without substantial agitation thereof and under a low differential pressure, to displace therefrom the liquid constituents contained therein.

.11. The process of separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises producing a wax-containing mixture, cooling said mixture to effect crystallization of wax to form a wax mass containing less than substantially 10% by volume of solid wax, and displacing from said mass, without substantial agitation thereof and under a relatively low differential pressure, the liquid constituents of said mass with such quantity of displacing liquid that said liquid will completely enter the wax mass before displacement is completed.

JOSEPH A. ALEXANDER. 

